I recently started updating my blog again, including a spiffy new theme. Within a day, my blog had reverted back. I double-checked my settings and switched the theme to the new one again, and the same thing happened.

If this is happening to you, it might be a file permissions issue on your server. WordPress tries to be maybe a little too helpful in this case – it has a function called validate_current_theme() that tries to make sure required files for the theme exist and if not, reverts to the default theme that function uses the PHP function file_exists().

You may be able to fix the issue by using an FTP client or SSHing to your server and changing the file permissions of the theme’s style.css and index.php.

If that’s not helping, you can always change the name of the template dir to “default” – WordPress doesn’t do the switch if it thinks you are already using the default theme.

There’s an old joke about the Internet that’s important for two reasons. First the joke:

It’s important because it illustrates a key cultural and technological underpinning of the Internet: anonymity. The second reason it’s important is that it’s so old, printed in the New Yorker in 1993, which is basically old testament times in Internet years. So for decades, the web has allowed people to browse without telling or proving who they are. Though many sites would love if you created an account and logged in, the vast majority are perfectly happy to serve up pages to you without even knowing if you’re a person or a dog.

But there are many reasons to want to track a user from page to page or from site to site, and there are various ways to do it. The most common way involves cookies. Web developers need a way to create user sessions or else things users like (shopping carts, preferences, the ability to update your profile picture) are impossible to implement.

Cookies are pretty well understood, and users can turn them off or clear them out if they really want. Google Chrome, for example, has “Incognito Mode” which allows you to surf without saving cookies, history, etc. from session to session. Even with cookies off, though, maintaining a user session within a particular site by passing around a session id isn’t too hard. It’s trivial to do in PHP for example.

Most users are pretty comfortable with this state of affairs – Facebook knows who I am because I logged in, but I trust them. Amazon knows who I am but that’s cool because I’m shopping. Some other site doesn’t know who I am, but it knows that I’m the same person who clicked on the widget to change the language a couple minutes ago.

People start getting uncomfortable when you start tracking them across sites. People become even more uncomfortable when they no longer have control over their anonymity. Three recent techniques violate both of those comfort zones in limited ways.

This doesn’t mean sites will know who you are, but they could use this information to know that you visited web page A, B and C whether or not you want them too. An ad network could use this info to track you across many sites. An unscrupulous site could sell this info, giving your browsing history away for cash, and if you log into a site that has personally-identifying info about you (email, shipping addresses, etc.) the history could potentially be tied back to a person.

Next post, I’ll talk about another way to track users without cookies and a way for a site to tell if you’ve visited other sites in the past. I’ll also tell you why you shouldn’t panic, though I admit a better writer would have told you that first.

Earlier I wrote about using Photoshop to create a heat map and to use data maps when house hunting. I got a pretty good response to those tutorials but the process is a little too labor intensive for most. So when I moved to California, I decided to do something similar, using the Google Maps API, so that it would be easy for anyone to make their own heat map.So here it is: Localographer – build interactive heat maps for house and apartment hunting. You can see a screenshot below:Localographer is a beta release right now, so watch out for bugs and random downtime. Also, I have to add a disclaimer: this is not an official Google project, this is something I did on my spare time. In fact, most of the work was done before I started working at Google in preparation for our move to California.The site takes you though a series of steps to build your map:

Pick your city and create your map;

Add places you’d like to be near (like your job or your school);

Add potential locations (houses, apartments, condos) to see how they compare.

I’ve got a ton of ideas for additional functionality, so hopefully I’ll have time to add more in the next few weeks. I’ll also be working on the site’s design, making it a bit more usable and interactive.Here’s how a map in Localographer compares to my Photoshop heat map of the Cleveland area (click on the images to see larger versions):In case you’re interested, the site was developed in PHP with a MySQL database. The maps use the Google Maps API with some hand-written functions to correctly draw the hot spots.Please take a look and let me know what you think. Post and problems, bugs, or new feature ideas in the comments below. Later I’ll post a poll so you can vote on new features and other enhancements.